<!-- <script>
  class Dog {
    constructor(name, age) {
      this.name = name;
      this.age = age;
    }
    run() {
      console.log(this.name + " 正在跑");
    }
  }

  let wc = new Dog("wangcai", 2);
  console.log(wc);
  wc.run();

</script> -->

<!-- <script>
  class Animal {
    constructor(name, age) {
      this.name = name;
      this.age = age;
    }
  }
  class Dog extends Animal {
    constructor(name, age) {
      super(name, age);
    }
  }

  let wc = new Dog("wangcai", 3);
  console.log(wc);



</script> -->

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <div class="box"></div>

  <label for="username">用户名：</label>
  <input type="text" id="username">
</body>
</html>